September 20 in History

The Battle of the Catalaunian Plains — sometimes called Chalons — in 451 AD was one of those rare days when everything turned on a single general's decision. Flavius Aetius commanded a coalition of Romans and Visigoths against Attila, whose forces had already burned their way across Gaul. Estimates put the combined armies somewhere between 200,000 and 300,000 men. Attila retreated. But Aetius, who needed Attila as a political counterweight against his own Visigoth allies, let him escape. Three years later, Aetius was stabbed to death by the Roman emperor he'd just saved.

Agnes of Poitou was regent of the Holy Roman Empire — ruling on behalf of her six-year-old son Henry IV — when she met Andrew I of Hungary to negotiate borders in a region that would eventually become Burgenland, Austria. It was a meeting between two struggling regimes: Agnes was managing a regency plagued by noble challenges, and Andrew was dealing with succession pressure from his own brother. The strip of land they discussed wouldn't have a defined national identity for another 800 years. Two monarchs in uncertain power met to draw a line that barely anyone today could find on a map.

Robert of Geneva earned the title "Butcher of Cesena" in 1377 when he hired the Breton mercenary company to massacre the population of Cesena — estimates range from 2,000 to 8,000 civilians dead. A year later, French cardinals elected him Avignon Pope Clement VII, splitting the Catholic Church into two simultaneous papacies. Rome had one pope. Avignon had another. Both excommunicated each other's followers. The Great Schism lasted 39 years and required a council to invent the concept of deposing a sitting pope. It started with a man who ordered a massacre.

Maurice of Orange's forces force the surrender of the Spanish garrison at Grave, securing a critical foothold in the southern Netherlands. This victory breaks Spanish momentum in the region and demonstrates the tactical superiority of Dutch siege warfare, shifting the balance of power in the Eighty Years' War.

Galileo was 69 years old and half-blind when he faced the Inquisition in 1633. He'd published his "Dialogue Concerning the Two Chief World Systems" the previous year — a book that argued, barely disguised, that Earth orbits the Sun. The Church had actually seen the manuscript before publication. He had permission, of a kind. But political winds had shifted, and the pope felt mocked. Galileo recanted. He spent the rest of his life under house arrest, going fully blind in 1638. In that darkness, he dictated his most important work on physics.

The Walking Purchase of 1737 was a fraud built on a forged document and athletic selection. Pennsylvania colonists claimed a 1686 deed allowed them land extending as far as a man could walk in a day and a half. Then they hired three of the fastest runners in the colony, cleared a path in advance, and one man covered 66 miles in 18 hours — nearly double what the Lenape had expected. The 1.2 million acres they seized included most of the upper Delaware River Valley. The Lenape called it a cheat for the rest of their history with Pennsylvania.

The rebels who captured Porto Alegre in 1835 were called Farrapos — 'ragamuffins' — by their opponents, a nickname they adopted. They declared a Rio-Grandense Republic and fought the Brazilian empire for ten years, an astonishing duration for a regional revolt. The war ended in 1845 with a negotiated peace that gave amnesty to everyone and reintegrated the province without punishment. The Farrapos got almost none of their political demands. But the war produced Garibaldi — the Italian radical who'd been fighting in Brazil — who took what he'd learned directly to the unification of Italy. A failed rebellion trained the man who made a nation.